Method for expansion of sand grain-shaped raw material

ABSTRACT

The invention relates to a method for the expansion of sand grain-shaped raw material ( 1 ) in which the raw material drops downwards through a substantially vertical heated shaft ( 3 ) provided with means ( 2 ) for heating, in which a shaft flow ( 4 ) prevails and to a dosing element ( 6 ) which can be connected to a substantially vertical shaft ( 3 ) and a conveying line ( 7 ). 
     In order to prevent the pressure fluctuations coming from the conveying line ( 7 ) in the area of the shaft ( 3 ), a dosing element ( 6 ) is attached between the shaft and the conveying ( 7 ) line, in which the quantity of granulate which goes over from the shaft ( 3 ) into the conveying line ( 7 ) is regulated via means for regulating so that a defined material collection of the granulate is formed as a buffer is the dosing element ( 6 ), which decouples the shaft flow ( 4 ) from the conveying flow.

FIELD OF THE INVENTION

The invention relates to a method for the expansion of sand grain-shapedraw material in which the raw material drops downwards through asubstantially vertical heated shaft provided with means for heating, inwhich a shaft flow prevails and to a dosing element which can beconnected to a substantially vertical shaft and a conveying line.

PRIOR ART

A method for producing an expanded granulate from sand grain-shaped rawmaterial is disclosed in WO 2013/053635 A1, where the object consists inadjusting a closed surface or the expanded granulate in a controllablemanner so that the expanded granulate exhibits no hygroscopicity orhardly any hygroscopicity. In addition, the possibility of specificallyinfluencing the surface structure of the expanded granulate andtherefore the roughness is to be provided. To this end, this documentproposes providing a plurality of independently controllable heatingelements arranged along the drop section of the sand grain-shaped rawmaterial and performing a temperature detection along the drop section,wherein the heating elements are controlled depending on the detectedtemperature below the region in which the expansion process takes place.Removal of the expanded granulate from the lower end of the drop sectionis ensured by means of a pneumatic conveying line into which the dropsection opens.

As a result of the vertical alignment of the shaft and as a result ofthe additional introduction or extraction of process gases accompanyingthe expansion process, flows occur inside the shaft which act on thesand grain-shaped raw material. In particular, the formation of anear-wall upwardly directed boundary layer flow has a positive effect onthe quality of the expansion process since this boundary layer flowprevents any baking of the sand grain-shaped raw material on the wall ofthe shaft. If the expansion shaft is closed towards the top, in additionto the upwardly directed boundary layer flow, a central downwardlydirected core flow is established. This core flow prevents some of theabove-described boundary layer flow and therefore results in baked-ondeposits. The influence of the core flow can be reduced by thehitherto-known extraction/in-blowing of process gas from/into the headregion of the shaft.

As a result of the direct connection of the shaft to a pneumaticconveying line, however, pressure fluctuations are produced, possiblycaused by the cleaning cycles of a filter in the conveying line whichare passed on directly to the air in the shaft. As a result, transverseflows are produced in areas of the shaft, which impede the positiveeffect of the boundary layer flow and thus lead to baked-on depositswhich cause a substantial deterioration in the quality of the expansionprocess and which can only be eliminated by complex maintenance measureswhen the process is at a standstill.

Therefore the non-uniform expansion processes and the formation ofbaked-on deposits on the shaft walls can be seen as disadvantages of theprior art which occur as a result of transverse flows caused, forexample, by pressure fluctuations in the subsequent pneumatic conveyingline. The known extraction/in-blowing process gases from/into the headregion of the shaft cannot prevent this effect.

DESCRIPTION OF THE INVENTION

The formulation of the object forming the basis of the present inventionis to provide a method for producing an expanded granulate from sandgrain-shaped raw material and a dosing element for connecting the shaftto the conveying line, which does not have the described disadvantagesand ensures that the pressure fluctuations from the conveying line donot affect the quality of the expanded granulate. The method shouldensure trouble-free and low-maintenance operation. The dosing elementshould be characterized by a simple and reliably design. Furthermore, itshould be possible to retrofit the invention to existing systems withoutmajor expenditure.

This object is achieved by the method mentioned initially whereby adosing element is attached between the shaft and the conveying line, inwhich the quantity of granulate which goes over from the shaft into theconveying line is regulated via means for regulating so that a definedmaterial accumulation of the granulate is formed as a buffer in thedosing element, which decouples the shaft flow from the conveying flow.

The invention is based on the fact that as a result of an accumulationof material which can be formed by simple means, possibly by piling upthe granulate which drops down, pressure conditions can be establishedin the region above the material accumulation which in normal operationare no longer influenced by the pressure fluctuations in the conveyingline. It is self-evident that as a result of the formation of a materialaccumulation, no complete gastight sealing of the shaft with respect tothe conveying line can be achieved but the sealing effect is sufficientto prevent a transfer of pressure fluctuations from the conveying flowto the shaft flow.

By attaching means for regulation, the height of the materialaccumulation can be specifically influenced and adjusted to the optimalvalue for the current process where lower limits must not be fallenbelow and upper limits must not be exceeded.

With regard to the sand grain-shaped raw material, not only mineralsands can be used in which water is bound as propellant such as, forexample, pearlite or obsidian sand. This can also comprise mineral dustwhich is mixed with water-containing mineral binder where in this casethe water-containing mineral binder acts as propellant. The expansionprocess can in this case proceed as follows: the mineral dust whichconsists of relatively small sand grains having a diameter of, forexample, 20 μm, forms larger grains of, for example, 500 μm with thebinder. At a critical temperature the surfaces of the sand grains of themineral dust become plastic and form closed surfaces of the largergrains or melt to form such. Since the closed surface of an individuallarger grain is usually overall smaller than the sum of all the surfacesof the individual sand grains of the mineral dust which are involved inthe formation of this larger grain, in this way surface energy isobtained or the ratio of surface to volume decreases. At this moment,larger grains each having a closed surface are present where the grainscomprise a matrix of mineral sand dust as well as water-containingmineral binder. Since the surface of these mineral grains as previouslyare plastic, the forming water vapour can subsequently expand the largergrains. That is, the water-containing mineral binder is used aspropellant. Alternatively mineral dust can also be mixed with apropellant, where the propellant is blended with mineral binder whichpreferably contains water. CaCO₃ for example can be used as propellant.In this case, the expansion process can take place similarly to thatdescribed above: the mineral dust which has a relatively small sandgrain size (for example, 20 μm diameter) forms larger grains (forexample, 500 μm diameter) with the propellant and the mineral binder.Upon reaching a critical temperature, the surfaces of the sand grains ofthe mineral dust become plastic and form a closed surface of the largergrains or fuse to form such. The closed surfaces of the larger grainsare plastic as previously and can now be expanded by the propellant. Ifthe mineral binder is water-containing, this can function as additionalpropellant. Thus, in a preferred embodiment of the method according tothe invention it is provided that the mineral material with propellantcomprises a mineral material in which water is bound and acts aspropellant or mineral dust mixed with water-containing mineral binderwhich acts as propellant or mineral dust mixed with a propellant whichis blended with mineral binder, wherein the mineral binder preferablycontains water and acts as additional propellant. In order to be able tocarry out the method presented as efficiently as possible, in additionto a shaft furnace it is preferable to provide a plurality of heatingzones with (independently of one another) controllable heating elementsas well as an intelligent regulating and control unit. This controls theheating elements preferably as a function of measured temperatures alongthe furnace shaft.

The method according to the invention can for example be configured asin WO 2013/053635 A1. Its disclosure is therefore incorporated fully inthis description.

A preferred embodiment is characterized in that the materialaccumulation which serves as a buffer is designed in such a manner thatat least a first cross-section of the dosing element is filledcompletely with expanded granulate from the shaft over a defined height.This type of buffer is characterized in that it is particularly simpleto produce. The expanded granulate dropping from the shaft is piled upuntil a certain height has been reached and the material accumulationthereby forming serves as a buffer. The height of the materialaccumulation can, for example, be defined by the location of a measuringdevice which is attached in the dosing element and detects the presenceof a material accumulation. The location of the measuring devicecorresponds in the operating state of the dosing element to a certainheight within the dosing element and thus also to a certain height of amaterial accumulation then present.

According to a further preferred embodiment, the conveying flow isproduced by an extraction device. If the extraction system is attachedin particular at the end facing away from the dosing element, aconveying flow is obtained over the entire length of the conveying line,where other elements such as, for example, filter systems can beattached in the conveying line.

In another preferred embodiment, a separating device, preferably a gascyclone is provided in the conveying line by means of which the expandedgranulate is separated from the conveying flow. Since the expandedgranulate comprises the end product of the method, the concentratedremoval from the conveying flow, in particular by a gas cyclone, isadvantageous since in this way a container such as, for example, a silocan be filled in a simple manner for further transport or for furtherprocessing of the granulate.

A further preferred embodiment provides that the bulk density of thegranulate is determined as a quality feature of the expansion process inorder to subsequently regulate the means for heating or reduce thefeeding of raw material. Through continuous control of the expandedgranulate, such a procedure enables conclusions to be drawn on theconditions in the shaft. If the bulk density differs appreciably fromthe set standard parameters, this can on the one hand be down to adifferent composition of the sand grain-shaped raw material, which canbe compensated by modification of the temperature in the means forheating or it can be down to baked on deposits on the inner sides of theshaft. If the latter case occurs, the feeding of raw material can bereduced, preferably stopped completely in order to be able to carry outmaintenance work.

According to a further particularly preferred embodiment, the means forregulating increases or reduces the conveyed quantity of expandedgranulate in the conveying line by means of a local influencing of theconveying flow in the dosing element. Such a regulation of the conveyedquantity can be achieved without moving parts which come in contact withthe expanded granulate and is thus resistant to blockages. A reductionin the conveyed quantity leads to an increase in the materialaccumulation whereas the opposite case occurs when the conveyed quantityis increased.

In a further particularly preferred embodiment, the height of thematerial accumulation in the dosing element is detected and thisinformation is transmitted to the means for regulating. As a result, theheight of the material accumulation can be varied by the influence ofthe conveyed quantity or a non-uniform feeding of raw material can becompensated so that the height of the material accumulation remainsapproximately constant.

According to a further preferred embodiment, process air is extractedfrom the head region of the shaft in order to increase and therebystabilize the part of the shaft flow directed to the head region. As aresult of such a design, the positive effect of the lack of pressurefluctuations is combined with a reduction of the downwardly directedcore flow with the result that the flow conditions in the shaft can bekept largely constant independently of external influences.

A further preferred embodiment of the invention provides that processair is blown in or sucked into the head region of the shaft in order tostabilize the part of the shaft flow directed to the head region. Thisprovides another possibility for keening the flow conditions in theshaft approximately constant and has a positive effect on the quality ofthe expanded granulate as a result of the simultaneous reduction of thepressure fluctuations coming from the conveying line.

The dosing element according to the invention is characterized in thatit comprises a material container which can be connected to the shaftvia a shaft connection and has a longitudinal axis, a conveying sectionwhich can be connected to the conveying line via a conveying connectionand means for regulating which are configured so that a materialaccumulation is produced in the area of the material container whengranulate enters into the material container. The dosing element can beconnected to the shaft by the shaft connection so that expandedgranulate enters into the material container. Via the conveying sectionthe granulate reaches the conveying connection by means of which thedosing element can be connected to the conveying line in order to ensurethe removal of the expanded granulate which has passed through thedosing element. The conveyed quantity which passes through the dosingelement is influenced by the means for regulating in such a manner thata material accumulation forms in the material container since moregranulate drops from the shaft into the material container than isremoved from the dosing element via the conveying connection. If thematerial accumulation has reached a certain defined height, the quantityconveyed through the dosing element will approximately correspond to thequantity of granulate which drops from the shaft into the materialcontainer.

A system according to the invention can be configured so that thesubstantially vertically heatable shaft is connected via the shaftconnection to the material container of the dosing element in whichmeans for regulating the conveyed quantity are located and that theconveying section of the dosing element is connected to the pneumaticconveying line via the conveying connection.

The initially formulated object can thus be solved both by a dosingelement according to the invention alone and also by a system accordingto the invention containing the dosing element. Thus, the invention alsorelates to a system for carrying out a method according to the inventionwith a dosing element which is connected to a substantially verticalheatable shaft and a pneumatic conveying line, wherein it is providedaccording to the invention that the dosing element comprises a materialcontainer which is connected to the shaft via a shaft connection andwhich has a longitudinal axis, a conveying section which is connected tothe conveying line via a conveying connection, and means for regulatingwhich are configured so that a material accumulation is produced in thearea of the material container when granulate enters into the materialcontainer.

According to a preferred embodiment of the dosing element according tothe invention or a system according to the invention, the conveyingsection is guided through the material container transversely to thelongitudinal axis of the shaft. This type of connection of conveyingsection and material container is characterized in that no complexconstruction is required. The material container can, for example, bewelded together from sheet metal plates and must only be dimensioned sothat its dimensions are greater than the diameter of the conveyingsection.

In a further preferred embodiment of the dosing element according to theinvention or a system according to the invention, the conveying sectioncan be connected to the ambient atmosphere on the side opposite theconveying connection with the result that the extraction system canextract ambient air to produce the conveying flow and transport itthrough the conveying line.

According to a further particularly preferred embodiment of the dosingelement according to the invention or a system according to theinvention, on the side opposite the shaft connection, the conveyingsection has at least one opening to ensure transfer of expandedgranulate into the conveying section. Such a design ensures that thegranulate only enters into the conveying section by means of the suctioneffect of the conveying flow and that the granulate covers the longestpossible path before it reaches the at least one opening.

A further particularly preferred embodiment of the dosing elementaccording to the invention or a system according to the inventionprovides that a measuring device is attached in the area of the materialcontainer by means of which the height of the material accumulation canbe detected and which is coupled to the means for regulating theconveyed quantity. As a result, the conveyed quantity can be increasedor reduced according to the height of the material accumulation via themeans for regulating. If the height falls below a minimum height, theconveyed quantity is throttled and if a maximum height is exceeded, theconveyed quantity is increased.

According to a further particularly preferred embodiment of a dosingelement according to the invention or a system according to theinvention, the means for regulating the conveyed quantity is designed asan inner tube which is disposed inside the conveying section with abutterfly valve located therein. As a result of this simple design ofthe means for regulating, it is possible to regulate the conveyedquantity adjusting the valve. The inner tube preferably the same lengthas the conveying section and in the operating state is connected to theatmosphere on the same side as the conveying section so that ambient aircan also be sucked in through the inner tube. In addition, isadvantageous to attach the inner tube concentrically to the conveyingsection in order to achieve a uniform suction effect.

In a further particularly preferred embodiment of a dosing elementaccording to the invention or a system according to the invention, thebutterfly valve is configured so that it can be closed on the one handand thereby reduces the cross-section of the inner tube through whichflow takes place when an exceeding of a defined height of the materialaccumulation is detected by the measuring device in order to increasethe conveyed quantity and thus reduce the height of the materialaccumulation and on the other hand can be opened and thus increases thecross-section of the inner tube through which flow takes place when afalling below a defined height of the material accumulation is detectedby the measuring device in order to reduce the conveyed quantity andthus increase the height of the material accumulation. Since thebutterfly valve has the same diameter as the inner tube, a cross-sectionthrough which flow takes place can be adjusted. If the butterfly valveis normal to the longitudinal axis of the inner tube, there is nocross-section through which flow takes place and a strong suction isproduced in the area between the inner tube and the inner face of theconveying section, with the result that more expanded granulate issucked in from the material container. If the butterfly valve isparallel to the longitudinal axis of the inner tube, the same suctioneffect prevails over the entire cross-section of the conveying sectionand only a little granulate enters into the conveying section.

BRIEF DESCRIPTION OF THE FIGURES

A detailed description of a method according to the invention and adevice according to the invention now follows. In the figures:

FIG. 1 shows a schematic image of a system according to the invention,

FIG. 2 shows a detailed view of a dosing element according to theinvention,

FIG. 3 shows a sectional view of a dosing element according to theinvention along line AA in FIG. 2.

WAYS FOR IMPLEMENTING THE INVENTION

FIG. 1 shows a system for expansion of sand grain-shaped raw material 1.In this case, the raw material 1 falls through a vertical shaft 3 whichcan be heated by means 2 for heating, in the present embodiment aplurality of electrical resistance heaters 2 are used. The raw materialis fed in the head region 16 of the shaft 3. Since the resistanceheaters 2 can be controlled individually, a specific temperature profilecan be established along the shaft 3. As a result of the thermalradiation which acts on the raw material 1 from the shaft 3, the rawmaterial 1 expands to form expanded granulate 5. Due to the heated wallsof the shaft 3 and the ensuing process air 18, a shaft flow 4 isestablished in the shaft 3, which consists of a near-wall boundary layerflow in the direction of the head region 16 and a central core flow inthe direction of the shaft connection 20.

An additional extraction device 17 is provided in the head region 16 ofthe shaft 3, which extracts process air 18 from the head region 16 andthus improves the shaft flow 4. In addition, a control loop 30 iscoupled to the additional extraction device 17 which regulates thefraction of extracted process air 18 and sucked-in ambient air.Likewise, process air 18 can be blown into the head region 16 tostabilize the shaft flow 4 either by this additional extraction device17 or by another device not shown here.

Located at the lower end of the shaft 3 is a dosing element 6 whichregulates the quantity of granulate 5 conveyed from the shaft 3 into thepneumatic conveying line 7. The dosing element 6 has a shaft connection20 at the connecting point to the shaft 3 and a conveying connection 23at the connection point to the conveying line 7. Likewise a measuringdevice 15 is mounted in the part of the dosing element 6 adjoining theshaft 3, the measurement data of which is used to regulate the conveyedquantity.

An extraction device 12, which is preferably designed as a fan, ismounted at one end of the pneumatic conveying line 7 which sucks ambientair from the other end of the conveying line 7, which is designed to beopen to the atmosphere and this conveys expanded granulate 5. A gascyclone 13 is located inside this conveying line 7 via which granulate 5is separated from the conveying line. Located in the conveying line 7 isa filter system 28 which is preferably disposed between gas cyclone 13and extraction device 12 which separates small particles from theconveying line 7. By measuring the differential pressure by means of anadditional measuring device 29, the conveyed quantity of the extractiondevice 12 is controlled so that the flow velocity in the conveying line7 remains constant even when the filter system 28 is contaminated.

FIG. 1 shows that in this embodiment a weighing device 14 isadditionally provided, this being arranged downstream of the gas cyclone13 in relation to the flow of granulate 5 and can be used to determinethe weight and therefore the bulk density of the separated expandedgranulate 5. By means of this measurement, the quality of the expansionprocess can be assessed and accordingly the feeding of raw material 1 iseither reduced, preferably stopped entirely or the output of theresistance heaters 2 is increased in a specific region of the shaft 3.Alternative embodiments of the invention do not provide a weighingdevice 14 so that the expanded granulate 5 is introduced directly fromthe gas cyclone 13 into a container, preferably a silo.

FIGS. 2 and 3 now show a detailed view of the dosing element 6. FIG. 3shows one or the main functions of the dosing element 6: the formationof a material accumulation 10. Expanded granulate 5 falls from the shaft3 via the shaft connection 20 (FIG. 1) into a first part of the dosingelement, the material container 19 which has a longitudinal axis 21.Since the quantity of granulate 5 from the shaft in a first process stepis higher than the quantity of granulate 5 which enters into theconveying line through the dosing element 6, the material container 19is filled with expanded granulate 5 so that a material accumulation 10is formed which fills at least a first cross-section 11 of the materialcontainer 19. By this means the space located above the materialaccumulation 10 in the operating state, in particular the shaft 3, canbe decoupled in terms of pressure technology from the space locateddownstream of the material container 19 in the operating state, inparticular the conveying line 7, so that the pressure fluctuations inthe conveying line 7 do not affect the shaft flow 4. The materialcontainer 19 is designed so that it has at least the same cross-sectionas the shaft 3 in the area of the shaft connection 20, preferably theentire upper area of the material container 19 has the samecross-section as the shaft 3, which in particular is rectangular.

FIG. 2 shows that a conveying section 22, which preferably has acircular cross-section is guided through the lower region of thematerial container 19, which preferably has a larger cross-section thanthe shaft 3, wherein the largest diameter of the conveying section 22 isconfigured to be smaller than the smallest dimension of the interior ofthe material container 19. The distance between the outer side of theconveying section 22 and the inner sides of the material container 19 isa multiple of the largest diameter to be expected of a granule of theexpanded granulate 5 known from process-related empirical values.Usually the multiplication factor lies in a range between 10 times and100 times, preferably between 20 times and 40 times. Typical granulediameters of the expanded granulate 5 lie in the range of 0.5 to 5 mm.For example, for a granule diameter of 2 mm and a factor of 30, adistance of 2 mm×30, i.e. 60 mm is obtained.

The material container 19 therefore encloses at least a part of theconveying section 22, preferably the entire conveying section 22. Theconveying section 22 therefore preferably touches the base surface ofthe material container 19 and rests on this. The conveying section isguided transversely to the longitudinal axis 21 of the materialcontainer through this wherein in this variant of the inventions thelongitudinal axis 21 intersects the axis of the conveying section 22 ata point and the angle between the axes is 90°. Alternative embodimentsof the invention can also have different angles and offset axes. Inorder to ensure the transition of expanded granulate 5 from the materialcontainer 19 into the conveying section, at least one opening 24 (FIG.3) is provided in the conveying section 22. This at least one opening 24is located in this variant of the invention on the side of the conveyingsection 22 opposite the shaft connection 20 (and specifically on bothsides of the conveying section 22, here symmetrically to thelongitudinal axis 21), i.e. in the operating state on the lower sidewherein the at least one opening 24 is preferably designed as amultiplicity of slits. Alternative embodiments provide that the at leastone opening 24 has the shape of a rectangle, square or circle. In anycase, the at least one opening 24 must be dimensioned so that thegranules having the largest diameter which are known fromprocess-related empirical values can still pass through the at least oneopening 24 without a blockage forming. Preferably the ratio between thegranules and the diameter of the opening 24 lies between 1:3 and 1:100,particularly preferably between 1:5 and 1:50, in particular between 1:5and 1:25. For example, for a granule diameter of 2 mm and a ratio of1:5, the diameter of the opening 24 with 2 mm×5 is obtained as 10 mm.

Located in the inside of the conveying section 22 is a means 9 forregulating the conveyed quantity which in this variant is designed as aninner tube 25 with a butterfly valve 26. In this case, the largestdiameter of the inner tube 25 which like the conveying section 22 ispreferably circular, is smaller than the smallest diameter of theconveying section 22 and these two elements are arranged concentrically.By varying the cross-section and the position of the inner tube 25, manyalternative designs are feasible. The inner tube 25 is also, like theconveying section 22 and therefore the conveying line 7, connected tothe atmosphere on the side opposite the conveying connection 23 wherebyambient air can be sucked through all the aforesaid elements.

The butterfly valve 26 is disposed inside the inner tube 25 and ispreferably configured as a circular plate having a diameter which allowsthe closure of the inner tube 25. This butterfly valve 26 is rotatablymounted so that it is pivotable about an axis normal to the axis of theinner tube 25. This pivoting can take place in a region between a firstposition in which the butterfly valve 26 is parallel to the longitudinalaxis of the conveying section 22 and a second position in which thebutterfly valve 26 is normal to the longitudinal axis of the conveyingsection 22.

The same conveying flow 8 as in the conveying line 7 which is producedby the extraction device 12 (FIG. 1) prevails in the conveying section22. By means of this conveying flow 8 granulate 5 is conveyed from thematerial container 19 via the at least one opening 24 into the conveyingsection 22 and further into the conveying line 7.

If the measuring device 15 (FIG. 1), which monitors the height of thematerial accumulation 10 in the upper part of the material container 19in the operating state, detects that the height of the materialaccumulation 10 is too low, the butterfly valve 26 is opened, i.e.pivoted in the direction of the first position of the butterfly valve26. As a result, the cross-section 27 through which flow takes placewhen the second position is reached is the same size as the diameter ofthe inner tube 25 and the same flow velocity of the conveying flow 8prevails in the entire cross-section of the conveying section 22. As aresult little granulate 5 is transferred from the material container 19into the conveying section 22 and the height of the materialaccumulation 10 increases.

If the measuring device 15 (FIG. 1) now detects that the height of thematerial accumulation 10 is too high, the butterfly valve 26 is closed,i.e. pivoted in the direction of the second position of the butterflyvalve 26. As a result, the cross-section 27 through which flow takesplace when the first position is reached is minimal, preferablycompletely closed so that the flow velocity in the annular regionbetween the inner tube 25 and the inside of the conveying section 22becomes higher, with the result that a strong suction is produced and alarge quantity of granulate 5 is transferred from the material container19 into the conveying section and the height of the materialaccumulation 10 sinks.

This ensures that the height of the material accumulation 10 can alwaysbe held within a defined range in order to maintain the effect ofdecoupling of the shaft flow 4 from the conveying flow 5.

In this case, the minimum height of the material accumulation 10 isdetermined by the at least one opening 24 which must be covered withsaid minimum height. The actual height of the material accumulation 10which is established during operation is determined by means of thedistance of the measuring device 15 from the conveying section 22 whichis preferably 1 cm to 15 cm. The measuring device 15 (or its detector)should therefore at best be attached only slightly higher than theoutside diameter of the annular gap through which air flows (between theinner tube 25 and the inside of the conveying section 22) for sucking inthe expanded granulate 5.

REFERENCE LIST

-   1 Sand grain-shaped raw material-   2 Means for heating (electrical resistance heaters)-   3 Shaft-   4 Shaft flow-   5 Expanded granulate-   6 Dosing element-   7 Pneumatic conveying line-   8 Conveying flow-   9 Means for regulating-   10 Material accumulation-   11 First cross-section-   13 Gas cyclone (separating device)-   14 Weighing device-   15 Measuring device-   16 Head region-   17 Additional extraction device-   18 Process air-   19 Material container-   20 Shaft connection-   21 Longitudinal axis-   22 Conveying section-   23 Conveying connection-   24 Opening-   25 Inner tube-   26 Butterfly valve-   27 Cross-section through which flow takes place-   28 Filter system-   29 Additional measuring device-   30 Control loop

1. Method for the expansion of sand grain-shaped raw material (1) inwhich the raw material (1) drops downwards through a substantiallyvertical heated shaft (4) provided with means (2) for forming atemperature profile (3), in which a shaft flow (5) prevails wherein as aresult of the heat transfer in the shaft (4) the raw material (1)expands to expanded granulate (6) and the granulate (6) produced entersinto a pneumatic conveying line (7) with a conveying flow (8) forfurther transport, characterized in that the bulk density of theexpanded granulate (6) is measured continuously, wherein upon detectionof a deviation from at least one defined bulk density the temperatureprofile (3) in the shaft (4) is adapted automatically or manually and/orthe feeding of raw material (1) into the shaft (4) is reducedautomatically or manually, wherein the expanded granulate (6) isseparated by a separating device, preferably a gas cyclone (10), fromthe conveying flow (8) in the conveying line (7), wherein the bulkdensity of the granulate (6) separated by the separating device, inparticular the gas cyclone (10), is measured, wherein the separatedexpanded granulate (6) is concentrated to form a granulate flow (11) andsaid granulate flow (11) is guided into a measuring container (12),wherein the measuring container (12) is connected to a measuring device(13) configured as a weighing device to determine the bulk density andwherein the measuring container (12) has openings (21) in a base surface(17), through which at least one part of the granulate flow (11) drainscontinuously.
 2. The method according to claim 1, characterized in thatthe conveying flow (8) is produced by means of an extraction device (9).3. The method according to claim 1, characterized in that a dosingelement (14) is disposed between shaft (4) and conveying line (7). 4.The method according to claim 1, characterized in that process air (16)is extracted from the head region (15) of the shaft (4) in order tostabilize the part of the shaft flow (5) directed to the head region(15).
 5. The method according to claim 1, characterized in that processair (16) is blown into the head region (15) of the shaft (4) in order tostabilize the part of the shaft flow (5) directed to the head region(15).
 6. Device for measuring the bulk density of expanded granulate (6)according to the method of claim 1, the device comprising a separatingdevice configured as a gas cyclone (10), which can be connected to apneumatic conveying line (7), wherein at least one measuring container(12) which has a base surface (17) is disposed underneath the gascyclone (10) in the operating state for receiving at least a part of thegranulate flow (11) from the separating device configured as a gascyclone (10), wherein the measuring container (12) is connected to ameasuring device (13) for determining the bulk density, characterized inthat the measuring device is configured as a weighing device, preferablyas scales, and that the measuring container (12) has openings (21) inthe base surface (17), in order to allow at least a part of thegranulate flow (11) to drain continuously.
 7. The device according toclaim 6, characterized in that a means for concentrating the granulateflow (11), preferably a funnel (18), is disposed between the separatingdevice configured as a gas cyclone (10) and the measuring container(12).
 8. The device according to claim 6, characterized in that themeasuring container (12) is connected via a side arm (19) to themeasuring device (13).
 9. The device according to claim 6, characterizedin that an overflow (20) for at least one part of the granulate flow(11) is provided on the measuring container (12).
 10. System forperforming a method according to claim 1 with a device for measuring thebulk density according to claim 6, wherein the substantially verticallyheated shaft (4) is connected to the separating device configured as agas cyclone (10) via the pneumatic conveying line (7).